The killing of a German exchange student renewed international criticism of US 'stand your ground' self-defense laws. Police are investigating whether the alleged shooter set a trap for the student.

Daniel Reinhardt/AP

The soccer team of 17-year-old German exchange student Diren Dede holds a minute of silence prior to a soccer match in Hamburg, Germany. Celal Dede, the father of the student who was fatally shot in Montana, criticized US gun laws upon his arrival in the US.

New details in the case of a slain German exchange student suggest that teenage mischief may have played a role in a Montana shooting that has, once again, put US self-defense laws in the international spotlight.

In what’s turned into a peculiar American allegory involving marijuana, enhanced self-defense laws, and suburban crime fears, police say a 29-year-old Forest Service firefighter named Markus Kaarma shot and killed 17-year-old German exchange student Diren Dede on April 27 after the teenager apparently entered Mr. Kaarma’s open garage as part of a “garage-hopping” prank he learned from local Missoula kids, according to what a friend told police.

Kaarma’s live-in girlfriend told neighbors that someone had stolen marijuana from the firefighter’s garage stash on several occasions. Investigators say they removed a glass jar full of pot during the course of their investigation.

The shooting of Diren became an international incident as German diplomatic staff said “what happened [was] completely out of proportion to the probable risk.”

US prosecutors agree, already having charged Kaarma with homicide. An open question is whether a jury will believe police allegations that Kaarma set a trap for Diren by opening the garage door and linking up a baby monitor feed before shooting blindly into the darkened garage after spotting movement.

Kaarma is set to plead not guilty by self defense at an upcoming arraignment. Through his lawyer, he has said he was simply defending his home – including a 10-month-old baby and girlfriend – from a repeat burglar who may have posed an armed threat. His lawyer says the couple had the garage door open not to trap anyone but to air out cigarette smoke.

Some self-defense experts say the shooting may become a limit-tester for a new breed of self-defense laws debated ferociously since the killing of unarmed teenager Trayvon Martin in Sanford, Fla., in 2012.

So-called “stand your ground” laws are predicated on an English common law concept called the “castle doctrine,” where a homeowner has no duty to retreat from danger before engaging a perceived threat with deadly force. While more than 22 states have stand your ground laws that expand the castle doctrine to public spaces, all US states protect homeowners who use force reasonably to suppress an attack or intrusion by a stranger into the home.

But emerging facts – including police allegations that Kaarma “may have been impaired by alcohol, dangerous drugs, other drugs, intoxicating substances or a combination of the above at the time of the incident” – also suggest that the shoot-to-kill self-defense idea can blur the stakes of what in the past may have been minor, even mundane, confrontations.

“These controversies often involve a perfect storm of problems, where you have people who are angry and also people who feel empowered by [castle doctrine and stand your ground] laws,” says George Washington University law professor Jonathan Turley. “One of the most chilling aspects of these laws is that we’ve seen a fair number of shootings involving neighbors and children.”

The fact that Missoula police are pushing ahead with charges suggests a different tack than the one taken by US officials in a previous famous case of American self-defense becoming an international incident. In 1992, exchange student Yoshihiro Hattori was shot in Baton Rouge, La., after a homeowner mistook him for a criminal. The teenager was trying to find a Halloween party when he knocked on the wrong door. Prosecutors declined to bring charges.

Proponents of laws that allow the use of deadly force as long as motivations are reasonable say critics are trying to stir up irrational fears by using cases like the Montana shooting to paint new self-defense laws as dangerous.

“The first and most obvious error in attempting to apply stand your ground to [the Kaarma case] – indeed to ANY case taking place in or immediately around the defendant’s home – is that stand your ground is utterly irrelevant in that context,” writes Massachusetts attorney Andrew Braca on the “Legal Insurrection” blog. “The castle doctrine eliminates any otherwise existing duty to retreat if you are in your home, or its curtilage [immediate surroundings].”

But other self-defense experts argue that such assessments don’t factor in the broader social impact of stand your ground laws, which might be emboldening some Americans to forgo nuance and context in order to solve problems with gunfire.

“These new laws allow really aggressive use of force in an expanded set of circumstances,” says Mary Anne Franks, a law professor and self-defense law expert at the University of Miami. “What’s troubling is they say that before the fact, before you’re in a panic situation, you can plan to kill somebody.”

So far, US juries have struggled to define the limits of liberalized self-defense laws.

If the Kaarma case reaches trial, a jury will likely focus on whether the homeowner had reasonable fear of injury or death before opening fire, as well as whether there were other extenuating circumstances that fueled the killing.

Last week, a jury in Minnesota convicted Byron Smith of murder after he killed two teenage cousins that broke into his house in 2012. The jury objected to testimony about Mr. Smith’s apparently callousness after killing the duo and the fact that he appeared to have set a trap for the teenagers.

That verdict came after several high-profile verdicts where armed self-defense and proper use of force was a focus, including last summer’s acquittal in Florida of George Zimmerman, the neighborhood watch captain who shot and killed Trayvon after suspecting the unarmed teen was a thief. Trayvon was on his way home to where his dad was staying after buying some Skittles and an iced tea at a convenience store.

While the Zimmerman defense team did not include stand your ground in the defense, the judge in that case explained stand yourground self defense theory to the jury before deliberations began.